Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/134—Electrodes based on metals, Si or alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
  • H01M4/386—Silicon or alloys based on silicon
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
  • H01M4/621—Binders
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/64—Carriers or collectors
  • H01M4/66—Selection of materials
  • H01M4/661—Metal or alloys, e.g. alloy coatings
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
  • H01M4/40—Alloys based on alkali metals
  • H01M4/405—Alloys based on lithium
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery using the same. ⁇ Background technology
• lithium secondary batteries that use non-aqueous electrolytes and move lithium ions between the positive and negative electrodes to perform charging and discharging have been used as one of the new types of secondary batteries with high output and high energy density. .
• An object of the present invention is to provide a negative electrode for a lithium secondary battery, which can suppress the active material layer from peeling off from the current collector during charging and discharging, thereby improving the charging and discharging cycle characteristics.
• the purpose is to provide the lithium secondary battery used.
• the negative electrode for a lithium secondary battery according to the present invention comprises a silicon and / or silicon alloy.
• a negative electrode disposed an active material layer containing an active material particles and a binder on the surface of the conductive metal foil from Do that current collector containing, binder, tensile strength 50 N / mm 2 or more, elongation at break 10 % Or more, a strain energy density of 2.5 X 1 CI- 3 j Zmm 3 or more and an elastic modulus of 10,000 N / mm 2 or less.
• the current collector has mechanical properties of a tensile strength of 80 NZmm 2 or more, a proportional limit of 30 NZmm 2 or more, a breaking elongation of 1.0% or more, and an elastic elongation limit of 0.03% or more. Is preferred.
• the elastic extension limit is a strain at a proportional limit.
• the current collector and the binder have the above-mentioned mechanical properties, respectively. Since the current collector and the binder have the above-mentioned mechanical properties, even if the volume of the active material layer expands and contracts due to insertion and extraction of lithium, the active material layer does not peel off from the current collector. It is possible to suppress the decrease in the current collecting property in the electrode. Therefore, charge / discharge cycle characteristics can be improved. Since the current collector of the present invention has the above mechanical properties, even if a large force is applied to the current collector, it can be received within the range of elastic deformation.
• the current collector even if the current collector receives a large force due to expansion and contraction of the volume of the active material layer, it is possible to suppress the current collector from being deformed such as wrinkles.
• the active material layer is easily separated from the current collector.
• deformation of the current collector, such as wrinkles is unlikely to occur, so that peeling of the active material layer from the current collector can be suppressed.
• the binder in the present invention since the binder in the present invention has the above-mentioned mechanical properties, even if a large force acts on the binder due to expansion and contraction of the volume of the active material particles, it can be accepted within the range of elastic deformation ⁇ ⁇ . it can.
• the above mechanical properties of the current collector and the binder are values measured at 25 ° C. Further, the above mechanical properties can be measured using, for example, an Instron type 5566-universal testing machine manufactured by Instron.
• the tensile strength of the binder is more preferably 10 ON / mm 2 or more, and particularly preferably 50.0 N / mm 2 or more.
• the elongation at break is more preferably at least 50%, particularly preferably at least 100%.
• the strain energy density is more preferably 5 X 1 0- 3 J / mm 3 or more.
• Tensile strength and elongation at break can be determined from the stress and elongation at the time of sample breakage in a tensile test.
• the strain energy density is determined by the area under the stress-strain curve in the tensile test.
• the higher the strain energy density the more energy the binder can absorb before breaking.
• the elastic modulus of the binder as described above, 1 0 0 0 0 N / mm 2 or less but, more preferably 7 0 0 0 N / mm 2 hereinafter. If the elastic modulus of the binder is too large, it becomes difficult for the binder to relieve the stress caused by the expansion and contraction of the volume of the active material particles, and the current collecting property in the electrode is reduced.
• the current collector in the present invention is made of a conductive metal foil, its mechanical properties can be changed by heat treatment.
• the negative electrode is manufactured by arranging the active material layer on the surface of the current collector and then performing sintering between the active material particles in the active material layer and sintering the active material particles and the current collector.
• the above mechanical properties may be imparted to the current collector by the heat history of the sintering process. That is, the sintering process may be performed so that the current collector has the above-described mechanical characteristics. It is difficult to measure the mechanical properties of the current collector after sintering in the state of a negative electrode with an active material layer provided on the current collector. It can be determined by applying to the body and measuring the mechanical properties of the current collector.
• the mechanical properties of the binder can be determined by preparing a sample film of the binder and measuring the mechanical properties of the film.
• a negative electrode is manufactured by sintering as described above, the same heat treatment as in the sintering is applied to the film, and the mechanical properties of the film after the heat treatment are measured. Mechanical properties can be determined.
• the active material layer is formed on the surface of the current collector.
• the current collector Prior to disposing the current collector, the current collector may be subjected to a heat treatment to impart desired mechanical properties to the current collector. In this case, the mechanical properties of the current collector can be directly measured by performing a measurement test on the heat-treated current collector.
• the processing temperature for performing the sintering treatment is preferably from 200 to 500 ° C, more preferably from 300 to 450 ° C.
• the temperature of the current collector when the heat treatment is performed is preferably 500 ° C. or less, more preferably 400 ° C. or less.
• both the sintering and the heat treatment are performed in a non-oxidizing atmosphere.
• the non-oxidizing atmosphere include an inert gas atmosphere such as argon, a nitrogen gas atmosphere, and a vacuum atmosphere. Further, a reducing atmosphere such as a hydrogen atmosphere may be used. Among these. But Al An inert gas atmosphere such as gon is preferably used.
• a spark plasma sintering method and a hot press method may be used.
• the element in the current collector when the negative electrode is sintered, the element in the current collector may be diffused into the active material particles of the active material layer by the sintering.
• the element (1) when the element (1) is contained in the surface of the current collector, the element (2) diffuses into the active material particles, so that the adhesion between the current collector and the active material layer can be improved.
• the current collector in the present invention may have the above-mentioned mechanical characteristics. Therefore, even without performing the sintering or the heat treatment, those having the above mechanical properties can be used without performing the sintering or the heat treatment.
• the thickness X of the active material layer is defined as the thickness Y of the current collector and the surface roughness Ra of the current collector, that is, the arithmetic average roughness Ra, and the relationship of 5 Y ⁇ X, and 250 Ra ⁇ . Les, preferably to have. By satisfying such a relationship, generation of deformation such as wrinkles in the current collector can be suppressed, and peeling of the active material layer from the current collector can be further suppressed.
• the thickness X of the active material layer is not particularly limited, it is preferably lOOO / zm or less, and more preferably 10 to 100m.
• the surface roughness Ra of the surface of the current collector on which the active material layer is disposed is preferably 0.2 ⁇ m or more.
• the contact area between the active material layer and the current collector can be increased, and the adhesion between the active material layer and the current collector can be improved. Can be done.
• the binder penetrates into the irregularities on the surface of the current collector, an anchoring effect is exerted between the binder and the current collector, so that higher adhesion can be obtained. For this reason, peeling of the active material layer from the current collector is further suppressed.
• the active material layer When placing the active material layer on both sides of the current collector preferably has a surface roughness R a of both sides of the current collector is 0. 2 am more.
• the surface roughness Ra is defined in Japanese Industrial Standards (JISB 0601-1994).
• the surface roughness Ra can be measured by, for example, a surface roughness meter.
• a current collector having a surface roughened may be used.
• Examples of such a surface roughening treatment include a plating method, a vapor deposition method, an etching method, and a polishing method.
• the plating method and the vapor phase growth method are methods in which a surface having irregularities is formed on a metal foil current collector to roughen the surface.
• Plating methods include an electrolytic plating method and an electroless plating method.
• Examples of the vapor deposition method include a sputtering method, a CVD method, and a vapor deposition method.
• Examples of the etching method include physical etching and chemical etching.
• Examples of the polishing method include sandpaper polishing and blasting.
• the current collector used in the present invention is not particularly limited as long as it is made of a conductive metal foil.
• the current collector include a metal foil of a metal such as copper, nickel, iron, titanium, and cobalt, or an alloy of a combination thereof.
• those containing a metal element that easily diffuses into the active material particles are preferably used.
• examples of such a material include a metal foil containing a ⁇ element, particularly a copper foil and a copper alloy foil. Since copper element is easily diffused into silicon by heat treatment, when sintering is applied to the negative electrode, improvement in adhesion between the current collector and the active material layer can be expected.
• a metal foil provided with a layer containing a copper element on the surface of the current collector may be used as the current collector. That is, a metal foil formed of a metal element other than copper and having a copper or copper alloy layer formed on the surface can be used.
• An example of such a metal foil ' is one in which a plating film of copper or a copper alloy is formed on the metal foil by an electrolytic plating method. Specifically, the surface of the nickel foil is covered with copper. Or a copper alloy plated film is formed.
• the thickness of the current collector is not particularly limited, but is preferably in the range of 10 to 100 / m.
• the upper limit of the surface roughness Ra of the current collector is not particularly limited, but the thickness of the current collector is preferably in the range of 10 to 100 Atm.
• the upper limit of the surface roughness Ra of the current collector is preferably substantially 10 am or less.
• the binder in the present invention has the above-described mechanical properties after the completion of the production of the negative electrode. Therefore, when the sintering process is performed on the negative electrode, the negative electrode must have the above mechanical properties after the sintering process. Therefore, when sintering is performed, a heat-resistant binder is preferably used.
• Polyimide is preferably used as such a binder. Examples of the polyimide include a thermoplastic polyimide and a thermosetting polyimide. Polyimides can also be obtained by heat treating polyamide acids.
• the polyimide obtained by the heat treatment of the polyamic acid is obtained by dehydrating and condensing the polyamic acid by the heat treatment.
• the imidization ratio of the polyimide is preferably 80% or more.
• the imidization ratio is the mole% of the produced polyimide relative to the polyimide precursor (polyamic acid).
• Those having an imidization ratio of 80% or more can be obtained by, for example, heat-treating a N-methylbirolidone (NMP) solution of polyamic acid at a temperature of 100 to 400 ° C for 1 hour or more. For example, when heat treatment is performed at 350 ° C, the imidization rate becomes 80% in about 1 hour and 100% in about 3 hours.
• NMP N-methylbirolidone
• the polyimide preferably has a number average molecular weight of 5,000 to 100,000, and more preferably 10,000 to 100,000. Suppei If the average molecular weight is low, the mechanical properties tend to decrease. Also, if the number average molecular weight is high, the viscosity becomes high, and handling may be difficult.
• the sintering temperature is preferably higher than the glass transition temperature of the binder.
• the glass transition temperature of the binder be lower than the temperatures of the sintering and the heat treatment when the sintering or the heat treatment is performed.
• the glass transition temperature of the binder is preferably lower than or equal to 450 ° C., and more preferably lower than or equal to 350 ° C.
• heat treatment at a temperature higher than the glass transition temperature allows the binder to be thermally fused to the current collector, thereby greatly improving the adhesiveness.
• Linear expansion coefficient of the binder one is preferably 0. 1 X 1 0 _ 5 ⁇ 3 0 X 1 0- 5 ° C- 1, more preferably 0. 8 X 1 0- 5 ⁇ : L 0 X 1 0 1. — 1 and particularly preferably 1.0 X 10 — 5 to 3.5 X 10 — 5 ° C -1 .
• the contact interface between the binder and the current collector may be Adhesion tends to decrease due to formation of stress and stress.
• the linear expansion coefficient of copper is 1. 6 X 1 0 one 5. Since it is 1, it is preferable to use a binder having a linear expansion coefficient close to this.
• the amount of the binder in the active material layer is preferably at least 5% by weight of the total weight of the active material layer. Further, the volume occupied by the binder is preferably at least 5% of the total volume of the active material layer. If the amount of binder in the active material layer is too small, the adhesiveness in the electrode by the binder may be insufficient. If the amount of the binder in the active material layer is too large, the initial charge may be difficult because the resistance in the electrode increases. Therefore, the amount of the binder in the active material layer is preferably 50% by weight or less of the total weight, and the volume occupied by the binder is preferably 50% or less of the total volume of the active material layer.
• a conductive powder can be mixed into the active material layer.
• a conductive permanent network of the conductive powder is formed around the active material particles, so that the current collection in the electrode can be further improved.
• the conductive powder those having the same material as the conductive metal foil can be preferably used. Specifically, it is an alloy or a mixture of metals such as copper, nickel, iron, titanium, and cold, or a combination thereof.
• copper powder is preferably used as the metal powder.
• conductive carbon powder can be preferably used.
• the amount of conductive ⁇ 4 powder added is preferably 50% by weight or less of the total weight with the active material particles. If the amount of the conductive powder is too large, the mixing ratio of the active material particles becomes relatively small, so that the charge / discharge capacity of the electrode becomes small.
• the active material particles used in the present invention include silicon and Z or silicon alloy particles. As a silicon alloy, silicon and at least one other Examples include solid solutions with the above elements, intermetallic compounds of silicon with one or more other elements, and eutectic alloys of silicon with one or more other elements. Methods for producing alloys include arc melting, liquid quenching, mechanical alloying, sputtering, chemical vapor deposition, and firing.
• examples of the liquid quenching method include a single-roll quenching method, a twin-roll quenching method, and various atomizing methods such as a gas atomizing method, a water atomizing method, and a disk atomizing method.
• the active material particles used in the present invention particles obtained by coating the surface of silicon and / or silicon alloy particles with a metal or the like may be used.
• the coating method include electroless plating, electrolytic plating, chemical reduction, vapor deposition, sputtering, and chemical vapor deposition.
• the metal that covers the particle surface is preferably the same metal as the conductive metal foil used as the current collector.
• the active material particles used in the present invention may include particles made of a material that alloys with lithium.
• Materials for alloying lithium include germanium, tin, lead, zinc, magnesium, sodium, aluminum, gallium, indium and alloys thereof.
• the average particle size of the active material particles is not particularly limited, but is preferably 1.0 ⁇ m or less, more preferably 50 ⁇ m or less, and most preferably 10 zm or less.
• the average particle size of the conductive powder used by adding to the active material particles is not particularly limited, but is preferably 100 ⁇ m or less, more preferably 500 ⁇ m or less. ⁇ m or less, and most preferably 10 ⁇ m or less.
• the active material layer after forming the active material layer on the current collector, the active material layer
• a lithium secondary battery of the present invention is characterized by comprising the above-described negative electrode of the present invention, a positive electrode containing a positive electrode material, and a non-aqueous electrolyte.
• the solvent of the non-aqueous electrolyte used in the lithium secondary battery of the present invention is not particularly limited, but cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate, and dimethyl carbonate, methionoletinol
• cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate, and dimethyl carbonate, methionoletinol
• a mixed solvent with a chain carbonate such as carbonate and getyl carbonate is exemplified.
• a mixed solvent of the above-mentioned cyclic carbonate and an ethenol-based solvent such as 1,2-dimethoxetane and 1,21-jetoxetane is also exemplified.
• L i XF y (where X is P, As, S b, B, B i, A 1, G a, or In, and when X is P, As or S b, y is 6 and y is 4 when X is B, B i, Al, G a, or In), and lithium perfluoroalkylsulfonic acid imid L i N (C m F 2m + 1 S 0 2 ) (C n F 2n +1 S 0 2 ) (wherein m and n are each independently an integer of 1 to 4) or lithium perfluoroalkylsulfonate methide L i C ( C p F 2 p + 1 S 0 2 ) (C q F 2 q + 1 S 0 2 ) (C r F 2 A mixed solute with ( r + , SO 2 ) (where p, q and r are each independently an integer of 1 to 4) is preferably used.
• a mixed solute of L i PF 6 and L i N (C 2 F 5 S0 2) 2 is particularly preferably used.
• an electrolyte polyethylene O sulfoxide, polyacrylonitrile of any polymer electrolyte or gel polymer electrolyte impregnated with an electrolytic solution, L i I, inorganic solid electrolytes, such as L i 3 N is illustrated.
• the electrolyte of the lithium secondary battery of the present invention can be used as long as the lithium compound as a solute that develops ionic conductivity and the solvent that dissolves and retains the lithium compound are not decomposed at the time of charging, discharging, or storing the battery. Can be used without restrictions.
• the positive electrode material for lithium secondary battery of the present invention L i C o 0 2, L i N i 0 2, L i Mn 2 ⁇ 4, L i Mn0 2, L i C o 5 N i 5 O 2, L i N i. 7 C o. . 2 Mn. ., Lithium-containing transition metal oxides such as, metal oxides containing no lithium such as Mn 0 2 are exemplified.
• any other substance capable of electrochemically entering and releasing lithium can be used without limitation.
• FIG. 1 is a schematic cross-sectional view showing a lithium secondary battery produced in an example of the present invention.
• This negative electrode mixture slurry is applied to one side (rough surface) of an electrolytic copper foil (thickness: 35 ⁇ ) (current collector a 1) with a surface roughness Ra of 0.5 / m, which is a current collector. After drying, it was rolled. The obtained product was cut into a disc having a diameter of 2 Omm, and this was heat-treated at 400 ° C for 30 hours in an argon atmosphere, and sintered to obtain a negative electrode.
• the thickness of the sintered body (including the current collector) was 50 ⁇ . Accordingly, the thickness of the active material layer was 1, the thickness of the active material layer / the surface roughness of the copper foil was 30, and the thickness of the active material layer Z was 0.43.
• a polyimide was generated from the polyamic acid by the heat treatment, and the weight ratio of the polyimide in the active material layer was 18.2 weight 0 / o.
• the density of the polyimide was 1. lg / cm 3 , and the volume occupied by the polyimide was 31.8% of the total volume of the active material layer.
• Electrodeposited copper foil (collector a1 ) alone was heat-treated under the same conditions as above for electrode preparation (400 ° C, 30 hours in an argon atmosphere), and tensile strength, proportional limit, elongation at break , And the elastic elongation limit were measured. Table 1 shows these values.
• the thickness is a value measured with a micrometer
• the tensile strength, the proportional limit, the elongation at break, and the elastic elongation limit are the values measured using an Instron 5566-universal testing machine manufactured by Instron. It is. Further, the surface roughness Ra is a value measured by a surface roughness meter. table 1
• L i 2 C_ ⁇ 3 and C o C0 3 As a starting material, using L i 2 C_ ⁇ 3 and C o C0 3, L i: the atomic ratio of C o is 1: were weighed to be 1 were mixed in a mortar and the diameter 1 7m m After pressing with a metal mold and press-forming, the mixture was fired in air at 800 ° C. for 24 hours to obtain a fired body of LiCoO 2 . This was ground in a mortar to adjust the average particle size to 20 m.
• Figure 1 is a schematic cross-sectional view of the manufactured lithium secondary battery.
• the positive electrode 1 and the negative electrode 2 face each other with the separator 3 interposed therebetween. These are housed in a battery case formed by the positive electrode can 4 and the negative electrode can 5.
• the positive electrode 1 is connected to a positive electrode can 4 via a positive electrode current collector 6, and the negative electrode 2 is connected to a negative electrode can 5 via a negative electrode current collector 7, which allows charging and discharging as a secondary battery. It has a structure.
• electrolytic copper plating is applied to a rolled copper alloy (Cu-0.03 weight% Zr) with a thickness of 33 ⁇ m (surface roughness Ra: 0.1 ⁇ m).
• a battery A2 was produced in the same manner as in Experiment 1, except that a surface roughening treatment was performed to obtain a surface roughness Ra of 0.5 / m (current collector a2).
• the current collector a2 after the surface roughening treatment had a thickness of 35 m.
• the current collector instead of the current collector a1, the current collector was made of the same material as the current collector a1, the current collector had a thickness of 18 ⁇ m, and the surface roughness Ra was 0.5.
• Batteries A5 and A6 were produced in the same manner as in Experiment 1, except that the electrolytic copper foil (current collector a5) of Example 1 and the electrolytic copper foil (current collector a6) of 0.2 m were used.
• current collector a4 was used as the current collector, and the active material filling amount was changed.
• a battery A7 was made in the same manner as in Experiment 1, except that the thickness of the active material layer was 95 ⁇ .
• a battery A8 was prepared in the same manner as in experiment 1, except that the current collector a5 was used as the current collector, the active material filling amount was changed, and the thickness of the active material layer was 55 / m. Produced.
• the charge / discharge cycle characteristics of the batteries A1 to A8 and B1 were evaluated. Each battery was charged at 4.2 ° C at a current value of 1 mA at 25 ° C, and then discharged to 2.75 V at a current value of 1 mA, which was defined as one cycle of charging and discharging. . The number of cycles required to reach 80% of the discharge capacity in the first cycle was measured and defined as the cycle life. Table 5 shows the results. The cycle life of each battery is an index when the cycle life of battery A1 is 100.
• the thickness of the negative electrode after the charge / discharge cycle test was measured with a micrometer, and the change in the thickness of the negative electrode before and after the charge / discharge cycle test was determined. Note that the thickness of the negative electrode was an average value of measured values at five different points in the negative electrode.
• the current collector bl is out of the scope of the present invention in the tensile strength, the proportional limit, and the elastic elongation limit.
• Table 5 in the battery B1 using the current collector b1, the electrode thickness change before and after the test was larger than that in the batteries A1 to A8 according to the present invention. It can be seen that wrinkles are occurring. Battery B1 has lower cycle life characteristics than batteries A1 to A8 according to the present invention. Therefore, by using the current collector having the mechanical characteristics defined in the present invention, the current collector receives a large force generated by expansion and contraction of the volume of the active material particles due to occlusion and release of lithium. Even if the current collector does not deform such as wrinkles.
• the binder of the active material layer is not destroyed, and the deterioration of the charge / discharge cycle characteristics due to the deterioration of the current collecting property in the active material layer is suppressed.
• the ratio XZY of the thickness X of the active material layer to the thickness Y of the current collector is 5 or more.However, the change in the electrode thickness before and after the test is similar to that of the batteries A1 to A6. It is getting bigger.
• the ratio X / Ra of the thickness X of the active material layer to the surface roughness Ra of the current collector was 250 or more.
• Battery B2 was produced in the same manner as in Experiment 1, except that binder 1 was replaced by Noinder 31 (polyamide acid) in Experiment 1.
• polyimide was generated from polyamide acid by the heat treatment, and the weight ratio of polyimide in the active material layer was 18.2% by weight.
• a sample film was prepared by heat-treating only the binder under the same conditions as the above electrode preparation for the binders i1, 1, 2 and ⁇ 3, respectively, and the tensile strength was determined in the same manner as for the binder ⁇ 1.
• the elongation at break, strain energy-density, modulus of elasticity, glass transition temperature, coefficient of linear expansion, and thermal decomposition onset temperature were measured. Table 6 shows the results. Table 6
• the charge / discharge cycle characteristics were evaluated. Each battery was charged at 4.2 ° C at a current value of 1 mA at 25 ° C, and then discharged to 2.75 V at a current value of 1 mA. This was defined as one cycle of charging and discharging. The number of cycles required to reach 80% of the discharge capacity in the first cycle was measured and defined as the cycle life. Table 7 shows the results. The cycle life of each battery is an index with the cycle life of battery A1 in Experiment 1 being 100. Table 7
• the binder ⁇ 1 has an elastic modulus outside the range of the present invention. It has become.
• the battery B2 using the binder 1 had a shorter cycle life than the batteries Al, A9, and A10, indicating that the charge / discharge cycle characteristics were inferior. Therefore, when the binder has the mechanical properties specified in the present invention according to the present invention, the contact resistance between the active material particles increases due to the binder being ruptured due to the expansion and contraction of the volume of the active material particles. Also, it can be seen that peeling of the active material layer from the current collector is suppressed, a decrease in current collection in the electrode is suppressed, and a charge / discharge cycle is improved.
• the cycle characteristics of these batteries were evaluated in the same manner as described above.
• the cycle life is an index with the cycle life of battery A1 in Experiment 1 being 100.
• Table 8 also shows the cycle life of batteries A1 and A9.
• the batteries A1 and A9 sintered at a temperature higher than the glass transition temperature of the binder were the batteries A1 and A9 sintered at a temperature lower than the glass transition temperature of the binder. It can be seen that the charge / discharge cycle characteristics are superior to 11. This is because the heat treatment at a temperature higher than the glass transition temperature causes the binder to thermally fuse to the current collector, improves the adhesiveness between the binder and the current collector, and improves the current collector in the active material layer. It is considered that this was because the peeling from the surface was suppressed.
• the charge / discharge cycle characteristics are significantly reduced. This is considered to be because the binder was decomposed by the heat treatment at 700 ° C., and the adhesiveness of the binder in the electrode was greatly reduced, and the current collecting property was reduced.
• Binder A2 was subjected to a heat treatment (230 ° C, 30 hours) under the same conditions as the sintering of Battery Al1, and the mechanical properties were measured. It was shown to. When the binder al was heat-treated (700 ° C, 10 hours) under the same conditions as the sintering of Battery No. 3, the mechanical properties were measured because the binder was decomposed. I could not do it. Table 9
• Battery A12 was produced in the same manner as in Experiment 1, except that silver powder having an average particle size of 3 ⁇ m was added so as to be 20% by weight of the total amount with the silicon powder.
• the cycle characteristics of this battery were evaluated in the same manner as described above.
• the cycle life is an index when the cycle life of battery A1 is 100.
• Table 10 also shows the cycle life of battery A1.
• Table 10 As is clear from Table 10, the battery A12 added with silver powder has improved cycle characteristics as compared with the battery A1 added with no conductive powder. This is probably because the conductive powder formed a conductive network around the active material particles, thereby improving the conductivity in the active material layer.
• batteries A13 and A14 were produced in the same manner as in Experiment 1, except that silicon powder having an average particle size of 8 ⁇ m or 29 ⁇ m was used.
• the cycle characteristics of these batteries were evaluated in the same manner as described above.
• the cycle life is an index with the cycle life of battery A1 being 100.
• Table 11 also shows the cycle life of battery A1.
• Table 11 As is clear from Table 11, the cycle characteristics tend to be reduced by using a silicon powder having a large particle size. In particular, it is understood that the average particle size is preferably 10 / m or less.
• a current collector a7 was prepared by heat-treating an electrolytic copper foil (thickness: 35 ⁇ m) having a surface roughness Ra of 0.5 ⁇ under an argon atmosphere at 400 ° C. for 10 hours.
• the negative electrode mixture slurry was applied to one surface (rough surface) of the current collector a7, dried, and then rolled. Cut the obtained product into a disk shape with a diameter of 2 Omm Was. This was heat-treated at 170 ° C for 20 hours in an argon atmosphere for the purpose of improving the adhesiveness of the binder to the current collector, thereby forming a negative electrode.
• the thickness of the negative electrode (including the current collector) was up to 50. Therefore, the thickness of the active material layer was 15 ⁇ m, the ratio of the active material layer thickness / copper foil surface roughness was 30 and the ratio of the active material layer thickness / copper foil thickness was 0.43.
• the density of the polyimide was 1. lg / cm 3 , and the volume occupied by the polyimide was 31.8% of the total volume of the active material layer containing the polyimide.
• Table 12 shows the values of thickness, tensile strength, proportional limit, elongation at break, elastic elongation limit, and surface roughness Ra of current collector a7 that was further heat-treated at 170 ° C for 20 hours. Is shown. Table 1 2
• the current collector was the same as the current collector a7 except that the electrolytic copper foil used to produce the current collector a7 was not subjected to a heat treatment at 400 ° C for 10 hours (current collector A battery B5 was produced in the same manner as in the experiment 8, except that the body b2) was used.
• Table 13 shows the current, thickness, tensile strength, proportional limit, elongation at break, elastic elongation limit, and surface roughness R of the current collector b2 that was heat-treated at 170 ° C for 20 hours in an argon atmosphere. Indicates the value of a. Table 13
• a rolled copper alloy (Cu—0.03% by weight Zr) with a thickness of 33 m was used as the current collector (surface roughness Ra: O : 1 ⁇ m) is subjected to a surface roughening treatment by electrolytic copper plating to a surface roughness Ra of 0.5 ⁇ m and heat-treated at 400 ° C for 10 hours in an argon atmosphere.
• a battery A16 was made in the same manner as in Experiment 8, except that the body a8) was used.
• the thickness of the current collector a8 after the surface roughening treatment was 35 ⁇ m.
• Table 14 shows the values of thickness, tensile strength, proportional limit, elongation at break, elastic elongation limit, and surface roughness Ra of current collector a8 that was further heat-treated at 170 ° C for 20 hours. Is shown. Table 14
• Battery B5 and battery A16 were measured for charge / discharge cycle characteristics in the same manner as described above. The results are shown in Table 15. Table 15 As shown in Table 15, the battery B5 using the current collector b2 having no mechanical characteristics in the range of the present invention has low cycle characteristics. Therefore, since the current collector has the mechanical properties defined in the present invention, even if the current collector receives a large stress caused by the expansion and contraction of the volume of the active material particles due to the absorption and release of lithium, The current collector can mitigate this, and peeling of the active material layer from the current collector can be suppressed.
• Table 16 shows the thickness, tensile strength, proportional limit, elongation at break, elastic elongation limit, and surface roughness of the current collector a9 or a10 that was further heat-treated at 170 ° C for 20 hours. Indicates Ra. Table 16
• each of the current collectors a9 and a10 has the mechanical properties specified in the present invention.
• the cycle characteristics of these batteries were evaluated in the same manner as described above.
• the cycle life is an index when the cycle life of battery A15 is 100.
• Table 17 also shows the cycle life of battery A15.
• Table 17 As shown in Table 17, the batteries A17 and A18 using the current collectors a9 and a10 having the mechanical properties specified in the present invention show good cycle characteristics.
• a battery A19 was produced in the same manner as in Experiment 8, except that the electrode was not subjected to heat treatment after application of the negative electrode mixture slurry. Also, A battery A20 was produced in the same manner as in the experiment 8, except that the binder used in the experiment 8 was a thermoplastic polyimide (binder 5) having a glass transition temperature of 355 ° C instead of the binder 4. .
• binder 5 thermoplastic polyimide
• the cycle characteristics of the batteries A19 and A20 were evaluated in the same manner as described above.
• the cycle life is an index when the cycle life of battery A15 is 100.
• Table 20 also shows the cycle life of battery A15.
• the battery A15 with the electrode heat treated at a temperature higher than the glass transition temperature of the binder was the same as the battery A19 without the heat treatment and the heat treatment at a temperature lower than the glass transition temperature of the binder. It can be seen that the charge / discharge cycle characteristics have been improved as compared with the battery A20. This is considered to be because the heat treatment at a temperature higher than the glass transition temperature of the binder improved the adhesiveness between the binder and the current collector and suppressed the peeling of the active material layer from the current collector. .
• the cycle characteristics of these batteries were evaluated in the same manner as described above.
• the cycle life is an index when the cycle life of battery C1 is 100.
• Table 21 shows the results.
• Table 2 1 is an index when the cycle life of battery C1 is 100.
• ADVANTAGE OF THE INVENTION According to this invention, it can suppress that an active material layer peels from a collector at the time of charge / discharge, and can use the lithium secondary battery which was excellent in charge / discharge cycle characteristics as a negative electrode.

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• 2003
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